Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

904
FXUS63 KLOT 172337
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
637 PM CDT Fri Jul 17 2026

.KEY MESSAGES...

- Scattered showers and non-severe thunderstorms are expected
  through sunset this evening.

- Hot and humid conditions continue Saturday afternoon.

- Scattered thunderstorms are expected to develop along a cold
  front Saturday afternoon and evening, some of which could be
  strong to severe.

- Wildfire smoke may return to the area in the wake of the cold
  front on Saturday and continue into Sunday.

&&

.DISCUSSION...
Issued at 305 PM CDT Fri Jul 17 2026

Showers with widely scattered thunderstorms continue this
afternoon across the area. 18Z DVN RAOB shows ample instability
and tall ELs in the region supportive of continued thunderstorm
development. However, weaker lapse rates amidst weak flow
through the column suggest they should maintain "airmass" or
pulse-like shower/storm behavior which has helped limit the
thunder coverage and lead to overall shorter duration with
individual cells. Renewed development is largely tied to
localized areas of convergence such as the lake breeze or any
outflow boundaries from nearby decaying showers/storms. The
general expectation is for this activity to continue through the
remainder of the afternoon with coverage starting to diminish
as we approach sunset this evening. Primary hazards include
lightning, torrential rainfall leading to ponding in poor
drainage spots and roadways, and gusty winds locally up to
around 50 mph with the strongest storms.

Focus then turns to Saturday as a mid-upper level shortwave
dives across the Great Lakes region. An associated surface cold
front is forecast to dive across the local area from midday
Saturday through early evening. This will serve as the focus for
scattered shower and thunderstorm development. Increasing mid-
upper flow with the incoming wave will support a damaging wind
threat with the strongest storms. Some uncertainty remains with
respect to how soon storms initiate along the front (between
~11am-1pm CDT) owing to an initial period of capping prior to
the arrival of steepening lapse rates with the mid-upper wave.
Coverage than increases through the remainder of the afternoon
from north to south.

Sunday is expected to be dry with the area situated between
systems. While Lake Michigan temperatures have warmed into the
mid-upper 70s, slightly cooler northeast to east winds off the
lake will help keep temperatures cooler than the past several
days in the upper 70s to lower 80s.

We are monitoring the potential for another round of strong to
severe thunderstorms late Monday into Monday night as another
wave dives across the area. A moist and unstable airmass
develops across the local area ahead of the associated cold
front. Stay tuned.


Smoke:

Southwest surface winds have helped to shift the greatest
concentrations of smoke north and east some and improve surface
visibilities, however, air quality remains in the "Unhealthy to
Very Unhealthy" AQI ranges for much of the area. Gradual
improvement may occur through the evening and overnight hours.
Smoke may return to at least portions of the area in the wake
of the aforementioned cold front Saturday afternoon and evening,
with smoke continuing into Sunday.

Petr

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 637 PM CDT Fri Jul 17 2026

Forecast concerns include...

Line of thunderstorms Saturday afternoon.
Wind shift to northeast Saturday afternoon.
Isolated showers this evening.
Wildfire smoke possibly returning Saturday evening.

Isolated showers will be possible through sunset, mainly east
and southeast of the Chicago terminals. An isolated thunderstorm
will also be possible well southeast of the terminals.

A cold front will move across the area Saturday afternoon and a
line of thunderstorms is expected to develop along/ahead of this
front in the early afternoon. The earlier the storms develop,
the farther north they will occur and opted to include prob
thunder mention at RFD and maintained tempo mention for the rest
of the terminals, though there is still uncertainty and storms
may develop just south of ORD/DPA. This line of storms is
expected to be fairly progressive, lasting 1-2 hours at any one
location, as it moves south through the mid/late afternoon.

Westerly winds may gust into the lower/mid 20kt range ahead of
the front/storms Saturday and then shift to the north/northwest
in the mid/late afternoon. Though a shift to the north/northeast
is expected for the Chicago terminals as the front moves south
down southern Lake Michigan. Gusts into the 15-20kt range will
be possible into Saturday evening.

With the return of northeast winds, the wildfire smoke that
remains over the northern Great Lakes may return to the local
area Saturday evening or Saturday night and given the expected
strength of the winds, opted to include smoke mention Saturday
evening for ORD/MDW. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT tonight for ILZ003-ILZ004-
     ILZ008-ILZ010-ILZ011-ILZ019.

     Air Quality Alert until midnight CDT Saturday night for ILZ005-
     ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

IN...Air Quality Alert until 1 AM EDT Saturday for INZ019.

     Air Quality Alert until midnight CDT Monday night for INZ001-
     INZ002-INZ010-INZ011.

     Air Quality Alert from 1 AM Sunday to 1 AM EDT Tuesday for
     INZ019.

LM...None.

&&

$$

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